// Service worker.
// Goal: keep the app usable on flaky/no network without ever serving stale DATA.
//   • App SHELL (HTML/CSS/JS/manifest) — network-first, fall back to cache so the
//     app still loads when offline. Successful fetches refresh the cache.
//   • API (/api/*) — never cached. The client handles offline itself (it queues
//     check-offs in localStorage and syncs on reconnect).

const SW_VERSION = 'v5';
const SHELL_CACHE = 'shell-' + SW_VERSION;
const SHELL = [
  '/', '/index.html', '/app.js', '/styles.css', '/md.js', '/manifest.webmanifest',
  '/vendor/motion.global.js'
];

self.addEventListener('install', (event) => {
  event.waitUntil(
    // Per-URL (not atomic addAll): one missing/404 entry must not reject the whole batch and
    // leave the new shell cache empty — otherwise a hard-offline navigation right after a
    // version bump would fall through to the offline page. allSettled caches what it can.
    caches.open(SHELL_CACHE)
      .then((c) => Promise.allSettled(SHELL.map((u) => c.add(u))))
      .catch(() => {})
  );
  self.skipWaiting(); // activate the new worker on next load
});

self.addEventListener('activate', (event) => {
  event.waitUntil((async () => {
    const keys = await caches.keys();
    await Promise.all(keys.filter((k) => k !== SHELL_CACHE).map((k) => caches.delete(k)));
    await self.clients.claim();
  })());
});

const OFFLINE_HTML =
  '<!doctype html><html><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>Offline</title><style>body{font-family:-apple-system,Segoe UI,sans-serif;background:#1a1a1a;color:#e0e0e0;display:flex;align-items:center;justify-content:center;height:100vh;margin:0;text-align:center;padding:20px;}h1{color:#3498db;margin-bottom:8px;}p{color:#b0b0b0;max-width:380px;}</style></head><body><div><h1>Offline</h1><p>The checklist needs an internet connection the first time. Try again when you\'re back online.</p></div></body></html>';

self.addEventListener('fetch', (event) => {
  const req = event.request;
  if (req.method !== 'GET') return;
  const url = new URL(req.url);
  if (url.origin !== self.location.origin) return; // third-party: passthrough
  if (url.pathname.startsWith('/api/')) return;     // never cache API; client handles offline
  // Full-resolution equipment photos can be several MB each and pile up fast; caching them
  // in the shell risks blowing the (small, all-or-nothing) iOS cache quota and evicting the
  // app shell. They already carry an immutable 1-year HTTP cache header, so let the browser's
  // HTTP cache handle them and keep them out of the shell cache entirely.
  if (url.pathname.startsWith('/equip-images/')) return;

  event.respondWith((async () => {
    try {
      const fresh = await fetch(req);
      // Cache successful shell/static GETs for offline fallback.
      if (fresh && fresh.ok && fresh.type === 'basic') {
        const cache = await caches.open(SHELL_CACHE);
        cache.put(req, fresh.clone());
      }
      return fresh;
    } catch (_) {
      const cached = await caches.match(req);
      if (cached) return cached;
      if (req.mode === 'navigate') {
        const idx = (await caches.match('/index.html')) || (await caches.match('/'));
        if (idx) return idx;
        return new Response(OFFLINE_HTML, { headers: { 'Content-Type': 'text/html; charset=utf-8' } });
      }
      throw new Error('Offline');
    }
  })());
});